Method and a measuring system for determining and monitoring exhaust gas emission from a vehicle

ABSTRACT

A method and a measuring system for determining exhaust gas emissions from a moving vehicle by a remote optical measuring technique. The model and/or type of the vehicle under examination is identified, and the driving situation of the vehicle in question is determined at the moment of measurement. A calculatory vehicle model is used to determine a case-specific estimate for the carbon dioxide concentration of the exhaust gas plume depending on the vehicle in question and its driving situation. The accuracy of determining the concentrations of the actual emission gases is improved by eliminating the inaccuracy of the carbon dioxide concentration values.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from Finnish patent application20010729 filed 9 Apr. 2001 and is the national phase of PCT/FI02/00283filed 3 Apr. 2002.

FIELD OF THE INVENTION

The invention relates to a method for determining and monitoring exhaustgas emissions from a moving vehicle or a corresponding object by remotemeasuring techniques. The invention also relates to a measuring systemfor implementing the afore-mentioned method.

BACKGROUND OF THE INVENTION

Exhaust gas emissions from traffic, particularly road traffic,constitute a significant part of harmful emissions caused by humanactivity to the environment. For example in 1998, exhaust gas emissionsfrom traffic made up about 50% of all emissions caused by the combustionof fossil fuels to the environment in Finland.

Certain upper limits are set by legislation for harmful exhaust gasemissions of vehicles used in road traffic, such as for the emissions ofcarbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NO_(x)) andfine particles. These limit values may vary according to the vehicle(type of vehicle and engine, age of vehicle) and, to some extent, alsoaccording to the country. The trend is to continuously and graduallyreduce said limit values as well as to bring them to a uniforminternational level. Authorities setting limit values for exhaust gasemissions include, for example, the Commission of the European Union andthe United States Environmental Protection Agency (US-EPA).

According to regulations addressed directly to vehicle manufacturers,new vehicles entering the market must fulfil the criteria for exhaustgas emissions which are valid at the time. The meeting of said criteriais controlled by means of various type approval tests. The type approvaltests include, for example, the measurement of exhaust gases during aspecific simulated test period including accelerations, decelerationsand stops when the vehicle is driven in a dynamometer. However, the typeapproval tests are only made for a number of vehicles before theapproval of said vehicle type/model for sale and use, wherein they cannaturally not be used to monitor the condition of vehicles which havealready been taken into use.

Of vehicles in actual use in road traffic, significant differences canbe found in exhaust gas emissions between different vehicles, due toe.g. the condition and/or age of the vehicles. Older vehicles and/orvehicles in poorer condition cause considerably higher emissions thannewer vehicles which are technically more developed and in goodcondition. Therefore, it can be stated that as the engine technology ofvehicles and the technology in the reduction of exhaust gases aredeveloped further and as the vehicle stock is simultaneously renewed,fewer and fewer old vehicles and/or vehicles in poor condition willcause a significant part of all emissions caused by vehicles.Investigators in the field have presented estimates that for example atpresent, about 10% of the vehicles cause about 50% of the CO emissionsfrom all the vehicles.

By reason of what has been presented above, the authorities shouldcontrol the observation of statutory limit values also vehicle byvehicle when the vehicles are already in use in road traffic. Typically,such a control is made in connection with the statutory inspections ofvehicles at regular intervals. In an inspection situation, as well as inmaintenance, exhaust gas emissions are typically measured during idlerunning or fast idle running, without substantially loading the engine.Consequently, this measuring method does not correspond to the normaluse of the vehicle in road traffic, with a varying load on the engine.Moreover, in several countries, for example in Finland, regular annualinspections of vehicles are only started after several years of theintroduction of a new vehicle. Therefore, the vehicle may, even beforethe first inspection or during the interval between the annualinspections, cause emissions which exceed the limit values but which arenot detected by the authorities.

Consequently, new measuring and monitoring methods are needed to monitorefficiently the exhaust gas emissions of single vehicles in a situationcorresponding to their normal use and irrespective of inspection timesor other predetermined times of testing. Various solutions are knownfrom prior art to use road-side measurement stations to determineemissions caused by single vehicles passing the measurement station, byremote measuring techniques directly when the vehicles are moving.

U.S. Pat. No. 5,498,872 (Stedman et al.) presents a solution for theremote measurement of exhaust gases from a moving vehicle. In thismethod, infrared (IR) and ultraviolet (UV) radiation is directed throughan exhaust gas plume emitted by a vehicle after the vehicle has passedthe measurement station. Means for emitting and detecting IR and UVradiation of the measurement station are placed on different sides ofthe lane along the road. The concentrations of said exhaust gases aredetermined on the basis of the absorption caused by the exhaust gasescontained in the emissions at the wavelength band specific to eachcomponent. The measurement of CO and HC concentrations is based on theabsorption in the IR range, and the NO concentration is measured bymeans of the absorption in the UV range.

U.S. Pat. No. 5,831,267 (Jack et al.) presents a method which largelycorresponds to said U.S. Pat. No. 5,498,872 but in which the measurementof the NO concentration is implemented in the IR range, wherein theapparatus becomes simpler, because a separate light source in the UVrange will thus not be needed.

In view of the present invention, said U.S. Pat. No. 5,831,267 (Jack etal.) can be considered to represent the closest prior art.

The measurement of exhaust gas emissions by the above-mentioned methodsbased on the absorption in the measuring beam is a demanding task,because one of the most important basic principles of absorptionspectroscopy is not fulfilled: the exact length of absorption range isnot known, because the precise shape of the exhaust gas plume is notknown and also the shape of the exhaust gas plume will vary quickly intime by the effect of e.g. turbulence and wind, as the concentrations ofthe exhaust gas plume are simultaneously diluted.

The use of absorption spectroscopy in measurements of gas concentrationis based on the known law of Lambert and Beer:I(λ)=I ₀(λ)e ^(−k(λ)x)  (1)

In Formula 1, I(λ) is the intensity of a measuring beam which has passedthe gas layer to be measured in an absorption length x, and I₀(λ) is theoriginal intensity of the measuring beam before the absorption caused bythe gas layer. The factor k(λ)[1/m] is an absorption coefficient whichdepends on the effective absorption cross-section Q(λ)[m²] as well as onthe gas concentration N [1/m³] according to Formula 2.k(λ)=Q(λ)N  (2)

In a situation, in which the effective absorption cross-section Q(λ) andthe absorption length x of the gas are known, it is possible todetermine the gas concentration N by means of the ratio I/I₀. Theeffective absorption cross-section Q(λ) can be determined by calibrationmeasurements made in advance, and/or its value for the gas in questioncan be found out in prior art.

Below, the term transmission will be used for the ratio I/I₀, which maythus receive values between zero and one.

In the above-mentioned solutions of prior art, Stedman et al. and Jacket al. base their measurements on the presumption that the distributionsand dilutions of CO₂ and the other emission gases CO, HC, NO_(x)contained in the exhaust gas are similar. Thus, by measuring thetransmission of the actual emission gases CO, HC, NO_(x) andsimultaneously the transmission of CO₂ in the IR range, it is possibleto determine, with high precision, the concentration of each emissiongas in relation to the concentration of CO₂.

Furthermore, Stedman et al. and Jack et al. presume that theconcentration of CO₂ in the exhaust gas is known and substantiallyconstant (independent of the driving situation), wherein by means of theconstant concentration determined for CO₂ it is also possible todetermine the absolute concentrations of the other measured emissiongases by means of the transmissions proportioned to the transmission ofCO₂.

To determine the concentration of CO₂ in the exhaust gas required insaid method, Stedman et al. and Jack et al. solve the stoichiometriccombustion equations. However, this approach involves a number ofvarious problems.

The first problem is that, to solve the combustion equations, it isnecessary to make presuppositions about the ratios between hydrogen andcarbon contained in the fuel and in the exhaust gases. Stedman et al.suppose that the ratio between hydrogen and carbon in both is 2:1. Jacket al. suppose that the ratio is 1.85:1 in fuel and 2.33:1 in exhaustgas. Although the presupposition of Jack et al. is more realistic, itdoes not take into account fuels with different compositions, such asfor example petrol and diesel oil, and thereby the differentcompositions of the exhaust gases.

Another problem of this approach is that the combustion in the enginesdoes not, by any means, always take place stoichiometrically.Nonstoichiometric combustion may occur in petrol engines for example insituations in which the engine and/or the fuel supply is defective, orthey have been intentionally modified, for example for a higher poweroutput. Petrol engines may thus operate with a too rich or too thinmixture with respect to a stoichiometric mixture of fuel and air.Because of their operating principle, diesel engines also normallyoperate with an excess of air; in other words, there is always an excessof air in relation to the fuel in the cylinder with respect to theconcentration required for stoichiometric combustion.

The third problem is that the above-mentioned approach completelydisregards chemical reactions taking place in a catalytic converterwhich is possibly used in the vehicle to change the composition of theexhaust gas.

The above description can thus be summarized by stating that todetermine the absolute concentration of CO₂ in exhaust gases, it willnot be sufficient to solve the stoichiometric combustion equations ingeneral, which will give, as the result, a constant value for theconcentration of CO₂ in the exhaust gases, irrespective of the drivingsituation. If the CO₂ concentration determined in this way is usedfurther to determine other emission gases by proportioning thetransmissions measured for them with the transmission of CO₂,inaccuracies will also be caused in the determination of theconcentrations of said other emission gases.

U.S. Pat. No. 5,583,765 (Kleehammer) presents a remote measuringtechnique intended particularly for heavy vehicles, to determine thetotal weight and exhaust gas emissions of a single vehicle, such as atrailer lorry, within allowed limit values. The measurement apparatus,which is preferably set up by the side of a road in a region where thereis an upgrade, makes it possible to collect following information abouta single vehicle and the measurement situation/site:

-   -   model/type data of the vehicle (dead weight, engine type,        transmission properties) for example by means of a bar code sign        placed in the vehicle for this purpose,    -   speed of the vehicle for example by means of a radar speedmeter,    -   ambient conditions at the measurement site, such as for example        air temperature, wind velocity, relative humidity, and air        pressure,    -   temperature of the exhaust gas plume for example by means of an        IR camera,    -   upslope of the road (gradient of the ascent) at the measurement        site,    -   chemical composition of the exhaust gas plume measured by        spectroscopy,    -   registration data of the vehicle, for example, by automatically        identifying the numbers on the registration plate from an image        which is taken of the vehicle.

The method of Kleehammer is essentially based on the presupposition thatthe temperature of the exhaust gas plume correlates with the poweroutput of the engine. In other words, the higher the power output of theengine, the higher the temperature of the exhaust gas plume. In themethod, the vehicle is identified, and the speed of the vehicle and thetemperature of the exhaust gas plume are determined when the vehicle isdriven uphill, wherein said speed and temperature can be used to obtaininformation about the power output of the engine of the vehicle. Thisinformation can further be used to determine the total weight and loadof the vehicle when the properties of the vehicle type in question (deadweight, engine type, power train), the slope of the hill and the otherambient conditions (air temperature, wind velocity, relative humidity,air pressure) are known.

In the method of Kleehammer, the chemical composition of the exhaust gasplume is also measured spectroscopically. Further, this measured profileof the exhaust gas emissions is compared with a reference profile whichcan be determined when the vehicle type and the power output of itsengine in the measuring situation are known. In U.S. Pat. No. 5,583,765,Kleehammer briefly mentions (e.g. column 5, line 60 to column 6, line 4)that the reference profiles of exhaust gas emissions can be based, forexample, on the limit values for the vehicle type in question, or onmeasurement data produced for the vehicle type by vehicle manufacturersor independent testing agencies. Furthermore, in U.S. Pat. No.5,583,765, Kleehammer does not describe in more detail, how thespectroscopic measurement of the chemical composition of the exhaust gasemissions is implemented.

In view of the present invention, it is essential that the measurementof the profile of exhaust gas emissions and the determination of thereference profile according to the Kleehammer method as presented inU.S. Pat. No. 5,583,765 are carried out as completely separateoperations and the profiles produced by them are only compared with eachother to determine, whether the exhaust gas emissions (measured profile)of the vehicle in question fall within the allowed limits. Theinformation contained in the reference profile is not utilized in anyway to improve the accuracy of the measuring result.

As the Kleehammer method is substantially based on the presuppositionthat the temperature of the exhaust gas plume correlates with the poweroutput of the engine, the method is primarily suitable for heavydiesel-engined vehicles only, which discharge an exhaust gas plume thatis sufficiently large and hot for accurate measurement of thetemperature of the exhaust gases. In vehicles equipped with a catalyticconverter, such as petrol-driven cars, the temperature of exhaust gasesdischarged from the exhaust pipe into the air does not corresponddirectly to the power output of the engine any longer but is primarilydependent on the operating temperature of the catalytic converteritself.

The primary aim of the present invention is to provide a new method fordetermining and controlling exhaust gas emissions from a moving vehicleor a corresponding object by a remote measuring technique, which methodmakes it possible to measure the absolute concentrations of emissiongases contained in the exhaust gas plume with a significantly higherprecision than in solutions of prior art.

It is also an aim of the invention to provide a measuring systemimplementing the aforementioned method.

In the solution according to the invention, the vehicle underexamination and its model/type are identified, and further, the drivingsituation of the vehicle is determined. Thus, by means of modeling, itis possible to determine the exhaust gas emissions, and particularly thecalculatory CO₂ concentration of the exhaust gases, from the vehicle,particularly in the driving situation in question.

The basic idea of the invention is that no predetermined constant valueis presupposed for the CO₂ concentration of the exhaust gases, but theestimate for the CO₂ concentration to be determined for the vehicle bycalculation may vary according to the vehicle in question and thedriving situation at the moment of measurement.

The calculatory value for the CO₂ concentration, determined in this wayand being more precise than in prior art, further makes it possible todetermine the actual harmful emission gases, such as CO, HC, NO, moreprecisely by absorption spectroscopy and by proportioning thetransmissions measured for said other emission gases with thetransmission of CO₂. In other words, the method according to theinvention solves the problem caused by the fact that the preciseabsorption length and/or the precise shape of the exhaust gas plumeand/or the dilution of the exhaust gases are not known. When theabsolute concentration of CO₂ is known, it is possible to determine, onthe basis of the optical transmission measured for CO₂, the so-calledeffective absorption length which is the same for all the emission gasesand which can thus be used to determine the absolute concentrations ofthe emission gases by means of the optical transmissions measured forthem.

In an advantageous embodiment of the invention, the optical absorptionscaused by all the emission gases to be examined, as well as by CO₂ whichis used as an indicator, are measured by measuring all said gasessubstantially at the same point in the exhaust gas plume and also bystoring the measuring signals substantially at the same time. This willimprove the accuracy of the measurement, because the composition andshape of the exhaust gas plume will thus be the same for all the gasesto be measured.

In an advantageous embodiment of the invention, also the NO measurementis performed in the IR range, wherein the measuring system becomessimpler, because there will thus be no need for a separate illuminatorin the UV range, optics and a detector. A known problem with NOmeasurement in the IR range is the strong absorption spectrum of watervapour falling in the same wavelength range and tending to interferewith the NO measurement. According to the invention, this problem isavoided by performing the NO measurement in the IR range by using aso-called correlation technique using an optical filter or filterarrangement as a wavelength filter in the reference and/or measuringchannel, wherein the transmission as a function of the wavelengthcorrelates with the comb-like structure of the spectral lines of theabsorption spectrum in the neighbourhood of 5.25 μm of NO. Because ofbetter selectivity which is thus achieved in the optical measurement,the effect of water vapour on the result of the NO measurement is thuseffectively minimized, and the sensitivity and accuracy of themeasurement are improved. Preferably, said filter means used is either aFabry-Perot comb filter or a so-called NO gas cell filter.

The most important advantages of the present invention include asignificant improvement in the accuracy of the measurement of emissiongases when compared with solutions of prior art. This makes it possibleto classify vehicles, for which the measurements have been taken, aspassing or violating the criteria set for exhaust gas emissions, with asmaller margin or error.

The invention improves the accuracy of measurement particularly forvehicles equipped with a catalytic converter and for diesel vehicles.

Furthermore, since the model and state of motion of the vehicle in themeasuring situation and under the measuring conditions are knownaccording to the invention, it is possible to use a calculatory vehiclemodel to determine the real fuel consumption of the vehicle at themoment of measurement, wherein it is further possible to determine thecoefficients of emissions of harmful gases for the vehicle, in the formof g/km (and/or g/s and/or g/kWh). The emission coefficients obtainablein this form can be used to evaluate the total emissions caused by thevehicles, and they make it possible to make a direct comparison, forexample, with results relating to the quality of air in urban areas. Ifthe fuel consumption of the vehicle is not known, then it is notpossible to convert the emission gas concentrations obtained by theabsorption measurement to said emission coefficients in a realiablemanner.

The following more detailed description of the invention to beexplicated with examples will more clearly illustrate, for anyoneskilled in the art, advantageous embodiments of the invention as well asadvantages to be achieved with the invention in relation to prior art.

BRIEF DESCRIPTION OF DRAWINGS

In the following, the invention will be described in more detail withreference to the appended drawings, in which

FIG. 1 shows, in principle, a measuring system according to theinvention,

FIG. 2 shows, in flow charts, an embodiment of the method according tothe invention,

FIG. 3 shows, in principle, an optical arrangement in the detectorsection of a spectrometer according to the invention,

FIGS. 4 to 6 illustrate, in principle, NO measurement according to theinvention by means of spectra,

FIG. 7 illustrates, in principle, an embodiment of a detector section ofa spectrometer for measuring NO, using an NO cell filter,

FIG. 8 illustrates, in principle, an embodiment of a detector section ofa spectrometer for measuring NO, using Fabry-Perot comb filters, and

FIG. 9 illustrates, in principle, the temporal behaviour of absorptioncaused by CO₂ in a measuring situation.

The appended drawings are only intended to illustrate the invention, andthus the structures and components shown in them are not drawn tocorrespond to their dimensions in reality. For the sake of clarity, thefigures do not show components and/or functions which are irrelevant andobvious for anyone skilled in the art as such.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The Measuring System and the Information Collected By It

FIG. 1 shows, in principle, the essential elements of a measuring systemaccording to the invention. The measuring system, which may be of a typeplaced stationary in its position or of a movable type, can comprisemeans and functions for storing following information about a vehicle 20moving along a road 10 in a data processing unit 30.

-   1) Means 60 for determining the optical absorption caused by the    gases CO, HC, NO, CO₂ contained in an exhaust gas plume 40 in a    measuring beam 50 on a wavelength band specific to each of said    gases. Said measurement is preferably made by means of a    spectrometer 60 placed along the road 10, the spectrometer 60    comprising an illuminator emitting IR radiation as well as optics    for directing the radiation emitted by said illuminator in a    substantially collimated measuring beam 50 to a reflector 70 placed    on the opposite side of the road 10. The reflector 70 will reflect    the measuring beam 50 along substantially the same route back to the    spectrometer 60, in which the measuring beam 50 is detected in a    spectrally resolved way.-   2) Means 80, 81 for measuring the speed and acceleration of the    vehicle 20. Preferably, said means comprise induction loops 80, 81    installed at regular intervals in the carriageway of the road 10.    The speed of the vehicle can be determined in a known way by    utilizing the time difference between the signals generated by the    front part and the back part of the vehicle in one induction loop.    By measuring the speed of the vehicle in the above-mentioned way at    two locations with two different induction loops, it is possible to    find out the acceleration of the vehicle. The information measured    in the above-mentioned way can also be utilized for classifying the    vehicle as a light vehicle (e.g. a car) or a heavy vehicle (e.g. a    trailer lorry). Naturally, it is obvious that the acceleration of    the vehicle can also be determined by another way obvious for anyone    skilled in the art, such as by a radar speed-meter based on radio    waves or laser light.-   3) Means 90 for determining the total weight of the vehicle 1.    Preferably, said means 90 comprise a piezo sensor or sensors    installed in the carriageway of the road 10. The information    measured in the above-mentioned way can also be utilized to classify    the vehicle as a light vehicle or a heavy vehicle.-   4) Means 100 for determining ambient conditions at the measurement    site, such as the air temperature, wind velocity, relative humidity,    and air pressure.-   5) Means 110 for identifying the vehicle 20. Preferably, said means    110 comprise a device for reading the registration plate on the    basis of a machine vision system.-   6) A function/means 120 for determining the profile (flat/slope) and    the roughness of the surface of the road 10 in the driving    direction. Preferably, the profile of the road 10 in the driving    direction is determined by the person installing the measuring    system, wherein said information, which remains substantially    constant, is simultaneously input in the data processing unit 30.    When the roughness of the surface of the road 10 is changed, for    example, because of snow or ice, the system may, if necessary, be    connected to functions based on machine vision, or the like, to    update the roughness data in the data processing unit 30.

The data processing unit 30 of the measuring system comprises softwarefor collecting said information from said means, as well as forprocessing and storing said information. Furthermore, the dataprocessing unit 30 can be in a data transmission connection with one ormore external systems for obtaining additional information and/orfunction commands, and/or for transmitting measurement data and/or datarelating to the functional status of the measuring system further.

From an external database (databases) 130, the data processing unit 30receives the model/type data of the vehicle 20 (dead weight, enginetype, transmission properties) on the basis of the data on theregistration plate of the vehicle 20. Preferably on the basis of thedata on the registration plate of the vehicle 20, information is firstretrieved from a so-called register database about the exact type and/ormodel of the vehicle, and then, by means of this type and/or model data,the more exact properties of the vehicle type in question are found outfrom a so-called type database.

Preferably, the data processing unit 30 is also connected to a datasystem 140 of the agency maintaining the measuring system, from whichthe measuring system receives function commands and to which themeasuring system can transmit messages relating to its own state, suchas notices of defects. To said external data system 140, the dataprocessing unit 30 can transmit statistical measuring data and/ormeasuring data relating to single vehicles, which the data system 140can transmit further to authorities or the like.

The Most Important Functions of the Measuring System

FIG. 2 shows, in flow charts, an embodiment of the method according tothe invention. The functions shown in FIG. 2 can be arranged to beperformed wholly in the data processing unit 30 or, for applicableparts, also in external data systems 130, 140, to which the dataprocessing unit 30 is connected.

In blocks 201, 202, 204, and 205 of the flow chart, the spectrometer 60measures the transmission of radiation in the IR range which has passedin a measuring beam 50 through an exhaust gas plume 40 at the differentabsorption wavelength bands specific to the gases CO₂, CO, HC, NO,wherein some possible average wavelengths are indicated in the blockcorresponding to each gas in FIG. 2. As it will be obvious for anyoneskilled in the art, the transmission measurement takes into account, ifnecessary, the properties of the different components (illuminator,detectors, optics) of the spectrometer 60 as well as the properties ofthe reflector 70 which are changed as a function of the wavelength.These so-called device functions can be stored in advance, for examplein the form of calibration curves, in the memory of either thespectrometer 70 or the data processing unit 30.

Furthermore, reference transmissions are separately measured for CO₂, COand HC at about 4 micrometres in block 203, and for NO at about 5.26micrometres in block 206.

Advantageously, the same common reference wavelength can be used forCO₂, CO and HC (block 203), because the absorption wavelengths of thesegas components are located sufficiently close to each other. Because thereference measurement in block 203 is not made at the absorptionwavelength of any given gas component, the measuring wavelength maydiffer to some extent from the 4 micrometres shown in FIG. 2. Thewavelength of the reference measurement can be selected to be suitable,for example in the range of 3.8 to 4 micrometres. It will be obvious foranyone skilled in the art that it is also possible to use referencemeasurements at several wavelengths, if necessary.

Except for the measurements related to NO in blocks 205 and 206, theabove-described measurements of the optical transmission of the gasesCO₂, CO and HC (blocks 201, 202 and 204) and the reference (block 203)can be made by any method and/or optical arrangement which will beobvious as such for a person skilled in the art.

For NO, the reference measurement is made separately at 5.26 micrometresin block 206, particularly to minimize the influence of water vapourcontained in the air and/or in the exhaust gas plume 40, as well as toimprove the sensitivity of the measurement. This will be described moreclosely below in connection with the more detailed description of the NOmeasurement according to the invention.

In block 200, the transmission signals recorded in the above-mentionedway substantially at the same time and at the same point in the exhaustgas plume 40 for the different gas components CO₂, CO, HC, NO and theirreferences are stored in the data processing unit 30.

If necessary, the attenuation caused in the measuring beam 50 byimpurities or the like in ambient air and/or in the exhaust gas plume 40is corrected in the transmissions measured in block 208 of FIG. 2. Suchimpurities include, for example, particles of dust or carbon black. Alsoother gas components as well as water vapour may cause undesirableabsorption at the measuring wavelength of the gas component underinvestigation. The correction is made, in practice, by computing theratio between the transmission under investigation and the referencetransmission. For CO₂, CO and HC, this is performed by means of thereference signal measured in block 203, and for NO, in turn, by means ofthe reference signal measured in block 206. In the case of NO, saidcorrection will efficiently include also the attenuation caused by watervapour in the measuring beam 50.

After the correction made in block 208 of FIG. 2, the real transmissionvalues (I/I₀, see Formula 1) are available for each gas CO₂, CO, NC, NO.These transmission values substantially indicate only the absorptionscaused by the exhaust gas plume 40 in the measuring beam 50 atwavelength bands corresponding to said gases.

In block 209 of FIG. 2, the transmission value determined for CO₂ in theabove-mentioned way is converted, for example by calibration factorspredetermined under laboratory conditions (block 210), to be indicatedas a value according to the unit concentration×absorption length(ppm×m).

The input data for the vehicle model in block 211 (vehicle model/typeand properties, speed, acceleration and weight of the vehicle, weatherand ambient conditions at the measurement site and in the measuringsituation) are used to determine a calculatory value for the absoluteCO₂ concentration in the exhaust gases of the vehicle in block 212. Bycombining, in block 213, the absolute CO₂ concentration (ppm) obtainedfrom the vehicle model and the measured value (ppm×m) determined forCO₂, it is possible, by means of the CO₂ and according to the invention,to determine the effective absorption length of the measuring beam 50 inthe exhaust gas plume 40.

After this, in block 214, by combining the data about said effectiveabsorption length and the calibration factors predetermined for theemission gases CO, HC, NO for example under laboratory conditions (block215), it is possible to compute the absolute values for said emissiongases as ppm values or the like.

Furthermore, an estimate for the fuel consumption of the vehicle at themoment of measuring (block 216) is obtained from the vehicle model(block 211). By combining the data about the momentary fuel consumptionof the vehicle and the composition of the exhaust gas plume 40 of thevehicle, it is possible, in block 217, further to determine the emissionfactors for each gas (CO, HC, NO, CO₂) contained in the exhaust gases ofthe vehicle, as values of emission gas mass per distance driven (g/km)and/or as emission gas mass per unit of time (g/s) and/or as emissiongas mass per engine output (g/kWh).

Furthermore, the data processing unit 30 can compare the emissionprofile (CO, HC, NO) measured in the above-identified way according tothe invention with the allowed limit values and, if necessary, transmitthe data to the authorities, or the like, controlling the matter.

The General Structure of the Spectrometer

FIG. 3 shows, in principle, one possible optical arrangement for thedetector section of a spectrometer 60.

The measuring beam 50, entering from the left in FIG. 3, is divided intodetectors DET1, DET1*, DET2, DET2*, DET3, DET3* by means of dichroicmirrors D1, D2 and beam splitters BS1, BS2, BS3. In front of each ofsaid detectors, a filter F1, F1*, F2, F2*, F3, F3* is used, to cut outthe radiation allowed to enter said detector more precisely.

Table 1 shows the properties of the essential components of thespectrometer according to FIG. 3.

The IR light source included in the spectrometer 60 is preferably forexample an infrared filament, a so-called globar or silicon carbide bar.These IR light sources emit radiation substantially according toPlanck's law of radiation, i.e. they act in the way of a so-called blackbody. As the IR light source, it is also possible to use any othersolution obvious for a person skilled in the art, including non-thermalradiators, such as LED's of the infrared range.

TABLE 1 Properties of essential components of the detector section inthe spectrometer 60 according to FIG. 3. D1 dichroic 45° mirror reflects5–5.5 μm (R1), transmits 3–4.8 μm (T1) D2 dichroic 45° mirror reflects4.3–4.8 μm (R1), transmits 3–4.2 μm (T1) BS1- beam splitter splittingratio 50/50, irrespective of BS3 wavelength F1 filter of NO measure-band pass filter (FIG. 7) or band pass ment band filter + Fabry-Perot(FIG. 8) - center wavelength of pass band 5.26 μm F1* filter of NOreference band pass filter + NO filter cell (FIG. 7) band or band passfilter + Fabry-Perot (FIG. 8) - center wavelength of pass band 5.26 μmF2 filter of CO measure- band pass filter ment band - center wavelengthof pass band 4.6 μm F2* filter of CO₂ measure- band pass filter mentband - center wavelength of pass band 4.41 μm F3 filter of referenceband band pass filter (CO, CO₂, HC) - center wavelength of pass bandabout 4.0 μm F3* filter of HCO measure- band pass filter ment band -center wavelength of pass band 3.4 μm

As the detectors DET1, DET1*, DET2, DET2*, DET3, DET3* in thespectrometer 60, it is possible to use, for example, PbSe detectors orMCT (Mercury Cadmium Telluride) detectors. The last mentioned ones areparticularly suitable for measurements at a wavelength exceeding 5 μm.

To detect IR radiation, it is advantageous to modulate the radiationemitted by the IR light source, for example, by a mechanical chopper,electrical optical modulator placed in front of the IR light source, orby alternating the electrical power to be supplied to the IR lightsource. By detecting the signal of the detectors DET1, DET1*, DET2,DET2*, DET3, DET3* at a narrow electrical pass band corresponding to thefrequency of said modulation, it is possible, in a way known as such, tofilter from the signals the background signals of other possible IRradiation sources in the visual field of the detector element, such asthose caused by the exhaust gas plume itself or other background. Thedetection can be performed in ways known as such by using, for example,a so-called lock-in amplifier, phase-sensitive detection or an adaptedfilter.

It should be noted that except for the measurement of the NOtransmission and reference signals according to the invention, based oncorrelation techniques, i.e. for example Fabry-Perot comb filters or aNO gas cell filter (blocks 205 and 206 in FIG. 2), the spectrometer 60can also be implemented in any other way obvious for a person skilled inthe art.

Naturally, it will be obvious for a person skilled in the art that thedesired wavelength bands for the detectors DET1, DET1*, DET2, DET2*,DET3, DET3* can also be arranged in other ways than by the opticalarrangement shown in FIG. 3. For example, by directing the measuringbeam 50 entering the detector section to pass through dichroic mirrorsplaced one after the other on the optical axis of the measuring beam 50,at an angle of 45 degrees to the measuring beam 50, it is possible touse each dichroic mirror to separate the necessary wavelength bandsdirectly to the detectors DET1, DET1*, DET2, DET2*, DET3, DET3* withoutusing separate band pass filters. This solution is advantageous formaximizing the optical signal, but it requires the use of dichroicmirrors whose wavelength bands are implemented particularly for thispurpose.

Furthermore, the measurements of the optical transmissions of the gasesCO₂, CO and HC (blocks 201, 202 and 204 in FIG. 2) and the reference(block 203 in FIG. 2) by the spectrometer 60 can also be implemented inother ways than the above-described ways based on the use of mirrors andband pass filters. The differentiation of the spectral bands on thedetectors can also be implemented by using, for example, a reflectiongrating, or further by any other way known as such. Thus, the term“spectrometer” must, in this context, be understood to refer to all suchoptical devices, by which it is possible to separate the desiredspectral bands corresponding to CO₂, CO, HC and the reference signalshown in FIG. 203 from the measuring beam 50 on different detectors in adesired manner. The spectrometer 60 used can also be a so-called FTIRspectrometer based on the fast Fourier transform.

The Implementation of the NO Measurement

In the following, we shall describe the solution for measuring theabsorption and reference signal for NO according to the invention, basedon correlation techniques, with reference to FIGS. 4 to 8.

In the wavelength range of 5.26 μm, the absorption spectrum of NOconsists of spectral lines recurring at regular, substantially constantwavelength intervals according to the curve 400 in FIG. 4. Whenmeasuring the absorption caused by NO in a wide wavelength band, forexample by means of a band pass filter with a transmission according tothe curve 700 in FIG. 4, the sensitivity of such conventionalmeasurement does not become very good, due to the narrowness of thespectral lines of NO in relation to the whole width of the measuringband.

The aforementioned problem, known as such from the absorptionspectroscopy to anyone skilled in the art, can be better understood bymeans of the following example.

In a situation, in which the NO concentration of the gas plume to bemeasured would be zero, the measuring result is a reference signal whichcorresponds to the area (indicated with A₀) left below the curve 400 inFIG. 4 when there are no absorption peaks caused by NO in the curve 400(in other words, the curve 400 is a horizontal line). In a situation, inwhich the NO concentration is 100 ppm-m as shown in FIG. 4, themeasuring result is a corresponding surface left below the curve 400(indicated with A). However, the difference here is that the spectralpeaks of NO are now included, reducing said area. Consequently, thetransmission of NO is now determined by means of the signalscorresponding to the ratio of the areas A/A₀. Since the ratio A/A₀ is,in this situation, the ratio between two almost equal numbers, themeasuring accuracy will thus become poor; in other words, the ratio A/A₀is only slightly changed with a change in the NO concentration, becauseA is changed only slightly. In practice, the reference signal should bedetermined as precisely at the same time with the absorption signal aspossible; therefore, the reference signal must be measured at such anadjacent wavelength band corresponding to the adsorption band of NO, atwhich NO is substantially not absorbent. This will further reduce themeasuring accuracy, because in this case the background caused by watervapour, which is always present to some extent in the gas plume to bemeasured and/or in the ambient air, is not precisely the same in thereference band and in the absorption measuring band; in other words, theabsorption caused by water vapour does not remain precisely constant asa function of the wavelength.

According to the present invention, said problem is solved by making theNO measurement by using, as the filter determining the measuring bands,such an optical filter or filter arrangement, in which the penetrationof said filter means as a function of the wavelength correlates with thecomb-like structure of the spectral lines of the absorption spectrumpresent in the vicinity of the 5.25 μm wavelength of NO.

According to the invention, said filter means used is preferably eitheran NO gas cell filter or a Fabry-Perot comb filter. It is thus possibleto measure the reference signal and the absorption signal precisely atthe same time, and particularly in the case of the Fabry-Perot combfilter, the sensitivity of the measurement is significantly improved,thanks to the narrow measuring band. Furthermore, since the absorptionsignal is measured at wavelengths which are in the direct vicinity ofthe wavelengths used in the measurement of the reference signal, thebackground absorption caused by impurities etc. and particularly watervapour contained in the air and/or in the exhaust gas plume is also moreprecisely taken into account.

FIG. 5 shows the transmission spectrum of an NO gas cell filter in asituation, in which the filter contains a high concentration of NO gas,for example 1%-m. In this case, the NO cell filter passes practically nolight at the wavelengths of the spectral lines of NO; in other words,the transmission at the spectral lines of NO is substantially zero, asshown in FIG. 5.

FIG. 7 shows an optical arrangement for measuring the reference andabsorption signals of NO utilizing an NO gas cell filter according tothe invention. The light coming to the NO measuring section of thespectrometer 60 is split with a beam splitter 1 into reference andmeasuring channels 702, 703 in such a way that light is directed to eachof said channels at pass bands with substantially equal width inwavelength. The width of the pass band covers at least partly or totallythe wavelength range, in which the NO line spectrum is present in thevicinity of 5.26 μm in the IR range. With respect to the intensity, thesplitting ratio of the beam splitter BS1 can, if necessary, differ fromthe splitting ratio 50/50, to achieve an optimal signal level for thedetectors DET1* and DET1. The filter F1* of the reference measuringchannel 702 comprises a combination of a wide band pass filter 700 (seeFIG. 4, curve 700) and an NO gas cell filter 701. Thus, the referencesignal measured by the detector DET1* is independent of the NOconcentration of the object to be measured. In a corresponding manner,the filter F1 of the measuring channel 702 comprises only a wide bandpass filter 700, which has preferably similar transmission properties asthe filter used for the reference channel 702. Now, the differencebetween the reference signal measured by the reference channel 702 andthe absorption signal measured by the measuring channel 703 is changedin proportion to the NO concentration of the object to be measured.

It will be obvious for a person skilled in the art that the filters 700,placed separately in the reference channel 702 and in the band passchannel 703 in FIG. 7 can, if desired, be replaced by placingalternatively one such filter before the beam splitter BS1. Furthermore,it will be obvious for a person skilled in the art that it is possible,if necessary, to install a so-called dummy filter in the measuringchannel 703, to bring the optical properties of the reference channel703 and the band pass channel 703 to correspond to each other (exceptfor the absorption of NO).

FIG. 8 shows an optical arrangement according to the invention, formeasuring the reference and absorption signals of NO by utilizingFabry-Perot filters (below, briefly FP filter).

The operation of the FP filter is based on an optical cavity formedbetween two end mirrors which are precisely aligned with each other andare partially light-transmitting. Depending on the wavelength of thelight guided through the end mirror into the cavity, the light issubjected to either constructive or destructive interference in thecavity. In the case of destructive interference, the light is nottransmitted through the cavity, but in the case of constructiveinterference, the cavity is substantially transparent. The principles ofoperation of the FP cavity and optical filters based on it are wellknown as such in spectroscopy, and they will therefore not need to bediscussed in more detail in this context.

According to the invention, for the measurement of the reference andabsorption signals, so-called FR comb filters 800, 801 are placed in thereference and measuring channels 802, 803, respectively. To limit themeasuring wavelength band, the reference and measuring channels 802, 803each also comprise wide band pass filters 700, whose transmissioncomplies substantially with the curve 700 of FIG. 4. In a correspondingway, in the situation of FIG. 8, said band pass filters 700 can also bealternatively replaced by one corresponding filter placed before thebeam splitter BS1.

The filter F1* of the reference channel 802 comprises an FP comb filter800, whose transmission curve is shown as curve 800 in FIG. 6. Thewavelength ranges recurring in the curve 800 of FIG. 6, i.e. the combtransmission peaks at which the FP comb filter 800 transmits light, arearranged, by suitable tuning of the FP cavity, to recur at intervalscorresponding to the gaps of the NO spectral peaks in such a way thatthe transmission ranges of the FP comb filter occur between the spectralpeaks of NO.

The FP comb filter can be tuned in a known way by altering the distancebetween the end mirrors of the cavity and/or by changing the angle ofincidence of light in relation to the FP comb filter, to affect theso-called free spectral range of the cavity and the distances betweenthe transmission peaks in the transmission spectrum of the FP filter.

In a corresponding manner, the filter F1 of the measuring channel 803comprises an FP comb filter 801, whose transmission curve is shown ascurve 801 in FIG. 6. The FP comb filter 801 of the measuring channel istuned so that the transmission ranges of the filter 801 overlap with thepeaks of the NO spectrum.

Now, the difference between the reference signal measured by thereference channel 802 and the absorption signal measured by themeasuring channel 803 is proportional to the NO concentration of theobject to be measured. With the measurement, a good sensitivity isachieved for the NO concentration, because the transmission wavelengthsand bands of the FP comb filter 801 of the measuring channel 803correspond to the wavelengths and width of the NO absorption spectrallines; in other words, a change in the absorption caused by NO willstrongly affect the quantity of light transmitted to the detector DET1.Furthermore, since the reference channel 802 is in the direct vicinityof the wavelengths used in the measurement of the absorption signal ofthe reference signal, the background absorption caused by water vapouris precisely taken into account.

In an advantageous embodiment of the NO measurement according to theinvention, the tuning of the FP comb filters 800 and 801 is fixed; inother words, the effective distance between the end mirrors of thecavity is arranged to be constant. Said effective distance between theend mirrors, experienced by the beam of light passing the FP cavity, canbe affected, in addition to the movement of the mirrors, by incliningthe FP comb filter in relation to the optical axis of the beam of lightpassing through it. In other words, by selecting the initial distancebetween the mirrors of the FP cavity in a suitable way so that thetransmission of the cavity recurs at intervals of the NO spectral lines,it is possible to finetune both FP comb filters 800 and 801 by alteringtheir angle with respect to the incident beam of light. The FP combfilter 800 is tuned so that its peaks come next to the NO absorptionspectral lines, and the FP comb filter 801 is tuned so that its peaksoverlap with the NO absorption spectral lines.

By this arrangement, it is possible to measure the reference andabsorption signals simultaneously by the optical arrangement of FIG. 8,in which separate FP comb filters 800, 801, tuned in a different,stationary manner, and separate detectors DET1*, DET1 are placed in boththe reference channel 802 and the measuring channel 801.

The FP cavities in the FP comb filters 800 and 801 can be implemented byusing either air (or another suitable gas) or a solid transparentmaterial as a medium between the end mirrors. Because the operation ofthe FP cavity is based on interference, even slight changes in thedistance between the end mirrors will affect the transmission of thecavity. Consequently, it is advantageous to use a ring, or the like,made of a material with a low thermal expansion coefficient (e.g.Zerodur®) as a spacer between the end mirrors in an FP cavity with anair medium. In a corresponding manner, an FP cavity with a solid medium,it is advantageous to use as the optical medium a material whose thermalexpansion coefficient is substantially equal to its thermal refractivitycoefficient in its absolute value but has a different sign. Such amaterial is, for example, barium fluoride (BaF₂), in which the change inthe optical distance caused by thermal expansion is compensated for bythe change in the refractive coefficient of the material.

The NO measurement according to the invention can also be implemented bya so-called scanning FP technique. Thus, only one FP comb filter withadjustable tuning is used instead of two separate FP comb filters withfixed tuning placed in the reference and measuring channels 802, 803.The adjustment of the tuning of the FP comb filter can be implemented ina way known as such, for example by a solution in which the distancebetween the end mirrors of the FP cavity is adjusted by piezo crystals.Thanks to this, fast temporal scanning of the transmission of the FPcomb filter becomes possible between the situations shown by the curves800 and 801 in FIG. 6, wherein either the reference signal or theabsorption signal can be detected by the detector at given moments oftime. If the scanning rate is, for example, in the order of hundreds ofherzes or kiloherzes, the reference and absorption signals can bedetermined in such a way that the time difference between the measuringof the reference signal and the measuring of the absorption signal is sosmall that, in practice, they correspond to measurements made at thesame time, wherein the properties of the object to be measured do notchange in this time. The use of a scanning FP comb filter has theadvantage that no separate reference and measuring channels will beneeded to measure the NO concentration, wherein the number of componentsin the apparatus is reduced.

Instead of using an NO gas cell filter or an FP comb filter, it is alsopossible to use any other filtering means whose transmission as afunction of the wavelength correlates with the comb-like structure ofthe spectral lines of the absorption spectrum present in the vicinity ofthe 5.25 μm wavelength of NO. Such a filter can also be implemented byusing, for example, diffractive optical gratings.

Furthermore, FIG. 9 illustrates, in principle, the temporal behaviour ofthe absorption caused by CO₂ in a measuring situation when the vehiclepasses the measuring beam 50. In the curve of FIG. 9, in the sectionindicated with reference number 901, the vehicle passes the measuringbeam 50 and prevents the entry of the measuring beam at the spectrometer60. In the section indicated with the reference number 900, theabsorption caused by the exhaust gas plume 40 of the vehicle in themeasuring beam 50, in this case the absorption of CO₂, is detected for ashort time (<0.5 s) during a period which starts when the vehicle hasmoved away from the measuring beam 50 and which ends when the exhaustgas plume 40 is dissolved by the effect of air turbulence caused by thevehicle, wind, etc. On the basis of FIG. 9, it is obvious that theoptical measurements to determine the gas concentrations of the exhaustgas plume 40 (blocks 201–206 in FIG. 2) must be made substantiallysimultaneously, wherein the composition and properties of the gas plume40 do not have time to change during the measurement.

If the measurements corresponding to the blocks 201–206 in FIG. 2 arealso made immediately before the vehicle enters the measuring point,i.e. in the section indicated with the reference numeral 902 in FIG. 9,it can be made sure that the vehicle in question really caused theemissions measured at the section indicated with the reference numeral900. If the emissions measured immediately before the entry of thevehicle at the measuring point are different from the normal prevailingquality of air, the measuring result can be marked as unreliable. Such asituation may occur, for example, when two vehicles drive closely oneafter the other and the emissions of the first vehicle, which areconsiderably larger than normal, do not have time to dissolve and diluteand are thus shown also in the measuring result of the followingvehicle.

It is, of course, obvious for anyone skilled in the art that bycombining, in different ways, the methods, modes of operation and devicestructures presented above in connection with different embodiments ofthe invention, it is possible to provide various embodiments of theinvention in accordance with the spirit of the invention. Therefore, theabove-presented examples must not be interpreted as restrictive to theinvention, but the embodiments of the invention can be freely variedwithin the scope of the inventive features presented in the claimshereinbelow.

For example, it is possible that in the future, regulated emissions fromvehicles are also determined to include other gases, such as benzene,1,3-butadiene or N₂O. The solutions according to the invention can alsobe applied in the measurement of such gases.

Furthermore, it will be obvious for a person skilled in the art that inthe blocks 201–206 of FIG. 2, it will not be quite necessary in allembodiments of the invention to determine the transmission valuesprecisely in the way defined in connection with Formula 1, but in somesituations, it is possible, in block 208, to proportion values of the“raw” signal, which are directly proportional to the transmission, witheach other without substantially reducing the accuracy of themeasurement.

1. A method for determining and monitoring exhaust gas emissions of amoving vehicle or a corresponding object by a remote measuringtechnique, the method comprising: forming a measuring beam of infraredradiation, which measuring beam is directed once or several timesthrough an exhaust gas plume emitted by the vehicle, determining, bymeans of the measuring beam, an optical measuring value for carbondioxide said measuring value indicating the optical absorption caused bycarbon dioxide contained in the exhaust gas plume in the measuring beam,determining, by means of the measuring beam, an optical measuring valuefor one or more actual emission gases each, said measuring valueindicating the absorption caused by said emission gas contained in theexhaust gas plume in the measuring beam, proportioning the opticalmeasuring values determined for the actual emission gases each with theoptical measuring value determined for carbon dioxide and solving, bymeans of an estimate determined for the carbon dioxide concentration ofthe exhaust gas plume, the concentrations of the actual emission gasesin the exhaust gas plume by means of said optical measuring values,wherein for the more precise determination of the actual emission gasesin the exhaust gas plume, the method further comprising: identifying themodel and/or type of the vehicle under examination, determining thedriving situation of said vehicle at the moment of measurement, andfurther forming a calculatory vehicle model for determining acase-specific estimate for the carbon dioxide concentration of theexhaust gas plume depending on the vehicle in question and its drivingsituation.
 2. The method according to claim 1, wherein the opticalmeasuring value determined for carbon dioxide and the case-specificconcentration estimate determined for carbon dioxide by means of thecalculatory vehicle model are used to determine the effective absorptionlength of the measuring beam in the exhaust gas plume, which is furtherused to determine the concentrations of the actual emission gases. 3.The method according to claim 1, wherein the optical measuring value,such as transmission, are determined for all the measured gasessubstantially at the same time and at the same point in the exhaust gasplume.
 4. The method according to claim 1, wherein the vehicle isidentified on the basis of the registration plate of the vehicle.
 5. Themethod according to claim 4, wherein the data contained in theregistration plate of the vehicle are used to retrieve the exact typeand/or model data of the vehicle from a register database.
 6. The methodaccording to claim 5, wherein the type and/or model data of the vehicleare used to retrieve more detailed information about the vehicle modelin question.
 7. The method according to claim 6, wherein said moredetailed information about the vehicle model in question comprises atleast one of the following: dead weight, engine type, and properties ofthe transmission apparatus.
 8. The method according to claim 1, whereinto determine the driving situation at the moment of measuring thevehicle, the speed and/or acceleration of the vehicle are determined. 9.The method according to claim 8, wherein the total weight of the vehicleand/or the weather conditions at the measurement site and time, and/orthe profile of the surface of the road in the driving direction at themeasurement site, and/or the roughness of the surface of the roadprevailing at the measurement site and time are also measured todetermine the driving situation at the moment of the measurement of thevehicle.
 10. The method according to claim 1, wherein the opticalmeasuring value for nitrogen oxide is determined in the infrared rangein the vicinity of the wavelength of 5.26 μm by using, for wavelengthfiltering or as part of the wavelength filtering in reference and/ormeasuring channels intended for NO, a filtering means whose transmissionas a function of the wavelength correlates with the comb-like structureof the spectral lines of the absorption spectrum present in the vicinityof 5.25 μm of nitrogen oxide.
 11. The method according to claim 10,wherein in each of the reference and measuring channels intended for NO,Fabry-Perot comb filters are used for the wavelength filtering or aspart of the wavelength filtering.
 12. The method according to claim 10,wherein in the measuring channel intended for NO, a scanning Fabry-Perotcomb filter is used for the wavelength filtering or as part of thewavelength filtering.
 13. The method according to claim 10, wherein inthe reference channel intended for NO, an NO gas cell filter is used forthe wavelength filtering or as part of the wavelength filtering, and, ifnecessary, a corresponding so-called dummy filter is used in themeasuring channel, to balance the optical properties of said channels.14. The method according to claim 1, wherein a calculatory vehicle modelis used to determine an estimate for the fuel consumption of the vehicleat the moment of measuring, which is used to convert the measuredemission values to emission coefficients in the form of g/km and/or g/sand/or g/kWh.
 15. The method according to claim 1, wherein measurementsare made for benzene and/or 1,3-butadiene and/or N₂O.
 16. A measuringsystem for determining and monitoring exhaust gas emissions from amoving vehicle or a corresponding object by a remote technique, thesystem comprising: means for forming a measuring beam of infraredradiation and for directing the measuring beam once or several timesthrough an exhaust gas plume emitted by the vehicle, means fordetermining, by means of the measuring beam, an optical measuring valuefor carbon dioxide said measuring value indicating the opticalabsorption caused by carbon dioxide contained in the exhaust gas plumein the measuring beam, means for determining, by means of the measuringbeam, an optical measuring value for one or more actual emission gaseseach, said measuring value indicating the absorption caused by saidemission gas contained in the exhaust gas plume in the measuring beam,means for proportioning the optical measuring values determined for theactual emission gases to the optical measuring value determined forcarbon dioxide, and means for solving the concentrations of the actualemission gases of the exhaust gas plume on the basis of the estimatedetermined for the carbon dioxide concentration of the exhaust gas plumeand said optical measuring values, wherein for the more precisedetermination of the actual emission gases in the exhaust gas plume, themeasuring system further comprising: means for identifying the modelandlor type of the vehicle under examination, means for determining thedriving situation of the vehicle at the moment of measuring, and furthermeans for forming a calculatory vehicle model for determining acase-specific estimate for the carbon dioxide concentration of theexhaust gas plume depending on the vehicle in question and its drivingsituation.
 17. The measuring system according to claim 16, wherein themeasuring system comprises means for determining the effectiveabsorption length of the measuring beam in the exhaust gas plume byusing an optical measuring value determined for carbon dioxide and acase-specific concentration estimate determined for carbon dioxide onthe basis of a calculatory vehicle model, as well as means fordetermining the concentrations of the actual emission gases by means ofsaid effective absorption length.
 18. The measuring system according toclaim 16, wherein the measuring system comprises means for determiningsaid optical measuring values for all the measured gases substantiallyat the same time and at the same point in the exhaust gas plume.
 19. Themeasuring system according to claim 16, wherein the measuring systemcomprises means for identifying the vehicle on the basis of theregistration plate of the vehicle.
 20. The measuring system according toclaim 19, wherein the measuring system comprises means for retrievingthe exact type and/or model data of the vehicle from a register databaseby means of the data contained in the registration plate of the vehicle.21. The measuring system according to claim 20, wherein the measuringsystem comprises means for retrieving more detailed information aboutthe vehicle model in question by means of said type and/or model data ofthe vehicle from a separate type database.
 22. The measuring systemaccording to claim 21, wherein said more detailed information about thevehicle model in question comprises at least one of the following: deadweight, engine type, and properties of the transmission apparatus. 23.The measuring system according to claim 16, wherein the measuring systemcomprises means for determining the speed and/or acceleration of thevehicle in the driving situation at the moment of measuring.
 24. Themethod according to claim 23, wherein the measuring system alsocomprises means for measuring the total weight of the vehicle and/or theweather conditions at the measurement site and time, and/or the profileof the surface of the road in the driving direction at the measurementsite, and/or the roughness of the surface of the road prevailing at themeasurement site and time.
 25. The measuring system according to claim16, wherein the measuring system comprises means for determining theoptical measuring value for nitrogen oxide at the infrared range in thevicinity of the wavelength of 5.26 μm in such a way that, for wavelengthfiltering or as part of the wavelength filtering in reference and/ormeasuring channels intended for NO, a filtering means is used, whosetransmission as a function of the wavelength correlates with thecomb-like structure of the spectral lines of the absorption spectrumpresent in the vicinity of 5.25 μm of nitrogen oxide.
 26. The measuringsystem according to claim 25, wherein the measuring system comprises, ineach of the reference and measuring channels intended for NO, aFabry-Perot comb filter with substantially fixed tuning for thewavelength filtering or as part of the wavelength filtering.
 27. Themeasuring system according to claim 25, wherein the measuring systemcomprises, in the measuring channel intended for NO, a scanningFabry-Perot comb filter for the wavelength filtering or as part of thewavelength filtering.
 28. The measuring system according to claim 25,wherein the measuring system comprises, in the reference channelintended for NO, an NO gas cell filter for the wavelength filtering oras part of the wavelength filtering, and, if necessary, a correspondingso-called dummy filter in the measuring channel, to balance the opticalproperties of said channels.
 29. The measuring system according to claim16, wherein the measuring system comprises means for determining, bymeans of a calculatory vehicle model, an estimate for the fuelconsumption of the vehicle under examination at the moment of measuring,and means for indicating the measured emission values as emissioncoefficients in the form of g/km and/or g/s and/or g/kWh by means ofsaid estimate for the fuel consumption.
 30. The measuring systemaccording to claim 16, wherein the measuring system comprises means forsetting up a data transmission connection and for data transmissionbetween the measuring system and one or more external systems.
 31. Themethod according to claim 16, wherein the measuring system alsocomprises means for taking measurements for benzene and/or 1,3-butadieneand/or N₂O.